Ocean Acidification: Effects on Morphology and Mineralogy in Otoliths of Larval Reef Fish

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If a larval fish cannot avoid predators and cannot orient itself in three-dimensional space, the consequences to the individual and the population are dramatic. Otoliths (ear stones), formed precipitation of calcium carbonate from a bicarbonate-rich and alkaline pH fluid, are critical to fish movement and orientation. Although marine fish compensate for carbon dioxide levels in the surrounding waters little is known about how increased dissolved carbon dioxide and changes in bicarbonate concentrations will impact the formation of otoliths. Increasing atmospheric carbon dioxide concentrations, leading to decreased ocean pH (ocean acidification) may have profound impact on the deposition, growth and function of these critical structures, particularly in larval fish. Focusing on pre-settlement age larval reef fish (Amphiprion clarkii and Chrysiptera parasema), this research integrates expertise in carbonate mineralogy, otolith development, and reef fish biology and leverages this unique combination of expertise to answer fundamental questions regarding the impact of ocean acidification on the structure and function of otoliths. Specifically, the research will answer two fundamental questions: What are the natural morphological and mineralogical variations within growing otoliths? How do these change when larvae are exposed to high dissolved carbon dioxide concentrations? Larvae will be hatched and reared under high carbon dioxide-induced low pH and three types of otoliths (sagittae, lapilli, asterisci) will be extracted over the duration of the experiments. Changes in calcium carbonate mineralogy from aragonite (most common) to vaterite (less common, less dense) as well as changes in crystal habit (well formed to poorly formed) will be evaluated using a combination of microscopic and morphometric techniques. The gap in understanding of otolith morphology and mineralogy precludes our ability to accurately evaluate the impact of ocean acidification on larval fish survival. Given that we know very little about the morphology and mineralogy of all three otolith types in larval marine fish, this research will provide fundamental data regarding natural variability. Data from unexposed and exposed larvae will inform our understanding of the development of otoliths and structure-function relationships. Additionally, otoliths provide long-term records of environmental life histories that could be better exploited if we understood the relation between environmental conditions and otolith morphology and mineralogy. This research represents a unique interdisciplinary collaboration between faculty and students at the University of Massachusetts Boston (a minority-serving institution), New England Aquarium (NEAq; not-for-profit research aquarium), and, through a formal partnership with NEAq, Roger Williams University (primarily undergraduate institution). NEAq is one of the premier visitor attractions in Boston, with over 1.3 million visitors a year, and a major public education resource. In addition to significant research outcomes this project also supports the development of informal science education materials that will be distributed to the public and displayed at the NEAq Harborside Learning Lab and NEAq Ocean Center. The project also supports the training of 1 PhD student and 1 undergraduate student.